1. Field of the Disclosure
The present disclosure relates generally to catalysts and processes involving them. The present disclosure relates more particularly to processes for regenerating catalysts for use in Fischer-Tropsch processes.
2. Technical Background
The Fischer-Tropsch process can be used for the conversion of synthesis gas (“syngas,” a mixture of H2 and CO) into liquid and/or solid hydrocarbons. The syngas can be made from a variety of feedstocks (e.g. natural gas, associated gas and/or coal-bed methane, biomass, residual oil fractions and coal). Fischer-Tropsch processes are conducted in a reactor in the presence of a suitable catalyst at elevated temperature and pressure to form paraffinic compounds ranging from methane to high molecular weight compounds comprising up to 200 carbon atoms, or, under particular circumstances, even more. Catalyst materials generally include an active component (e.g., a metal, often provided in the form of an oxide) supported on a catalyst support, which can be a porous refractory oxide such as alumina or silica. The support material can provide a high surface area upon which the active component can be dispersed and a pore network through which the reactant gases can diffuse in and the reaction products can diffuse out.
Catalysts become less active over time, thus making the catalyzed process less efficient. Loss of activity can occur via a variety of mechanisms. For example, the catalyst can be poisoned by a number of different species including, for example, sulfur, sodium, nitrogen or carbon containing compounds, all of which de-activate the catalyst. Accordingly, catalysts are replaced periodically in order to maintain acceptable product yield. However, as a result of the complex procedures and expensive metals (e.g., cobalt) used in catalyst fabrication, replacement of the catalyst can be quite expensive. Thus, it is more desirable to regenerate a catalyst (i.e., returning its activity to a desirable state) instead of replacing it, if possible. There exist methods in the art for regenerating Fischer-Tropsch catalysts; most involve removal of organic materials from the surface of the catalyst and reduction of the catalytic metal (e.g., cobalt) to a substantially metallic state. However, existing processes often do not completely reactivate a deactivated catalyst.
Thus, there remains a need to further improve the methods for regenerating catalysts used in Fischer-Tropsch processes.